The present invention relates to stabilizing fuel by deoxygenation, and more particularly to a fuel plate assembly for a fuel stabilization unit.
Fuel is often utilized in aircraft as a coolant for various aircraft systems. The presence of dissolved oxygen in hydrocarbon jet fuels may be objectionable because the oxygen supports oxidation reactions that yield undesirable by-products. Dissolution of air in jet fuel results in an approximately 70 ppm oxygen concentration. When the fuel is heated between 300 and 850° F. the oxygen initiates free radical reactions of the fuel resulting in deposits commonly referred to as “coke” or “coking.” Coke may be detrimental to the fuel lines and may inhibit fuel delivery. The formation of such deposits may impair the normal functioning of a fuel system, either with respect to an intended heat exchange function or the efficient injection of fuel.
Various conventional fuel deoxygenation techniques are currently utilized to deoxygenate fuel. Typically, lowering the oxygen concentration to 6 ppm or less is sufficient to overcome the coking problem.
One conventional Fuel Stabilization Unit (FSU) utilized in aircraft fuel systems removes oxygen from jet fuel by producing an oxygen partial pressure gradient across a membrane permeable to oxygen. The FSU includes a plurality of fuel plates sandwiched with permeable membranes and porous substrate plates within an outer housing. Each fuel plate defines a portion of the fuel passage and the porous plate backed permeable membranes defines the remaining portions of the fuel passages. The permeable membrane includes Teflon AF or other type of amorphous glassy polymer coating in contact with fuel within the fuel passages for preventing the bulk of liquid fuel from migrating through the permeable membrane and the porous plate.
The use of a plurality of similarly configured flat plates increases manufacturing efficiency and reduces overall cost. Further, the size and weight of the FSU is substantially reduced while increasing the capacity for removing dissolved oxygen from fuel. Moreover, the planar design is easily scalable compared to previous tubular designs.
Disadvantageously, the planar fuel plates are typically stainless steel which is relatively difficult, time-consuming, and expensive to machine while the oxygen permeable membrane is a relatively delicate, thin (˜2-5 microns) film which may lack mechanical integrity. Contact between the metallic fuel plate and the oxygen permeable membrane may result in damage to the permeable membrane which necessitates careful manufacture and assembly to avoid leakage between the multitude of plates.
A failed seal between plates or a damaged permeable membrane may permit inter-stream leakage which may dramatically decrease the performance of the FSU. Sealing the interface between fuel plates, sealing the fuel channel between fuel plates and the oxygen permeable membrane, as well as sealing the vacuum path from potential leaks to ambient are critical to effective operation of the FSU. Furthermore, to increase oxygen diffusivity and enhance fuel deoxygenator performance, the fuel plate includes a relatively intricate 3-dimension fuel channel structure which further complicates sealing and manufacture.
Although effective manufacturing techniques exist for the production of the relatively intricate 3-dimension fuel channel structure and the high-precision FSU sealing gaskets, these conventional techniques are exceedingly time consuming and expensive.
Accordingly, it is desirable to provide an effective relatively inexpensive and uncomplicated fuel plate and sealing gasket arrangement for a deoxygenation system that facilitates manufacture of an intricate 3-dimension fuel channel structure to increase fuel and deoxygenation.